Recently, with improvement in the line capacity of the Internet and development of elemental technology that deals with a variety of media information, we have come to enjoy information distribution of rich media using mobile terminals at anytime and anywhere. Since such a life style is widely accepted, as a high-speed mobile environment that supports the information distribution, a communication environment such as LTE (Long Term Evolution), is spread and expanding.
In this high-speed mobile communication environment, such as LTE, various techniques for increasing efficiency of data communications are introduced in the protocols of respective layers.
For example, in LTE, by OFDMA (Orthogonal Frequency Division Multiple Access) technique, a resource block consisting of 12 channels is subdivided by one millisecond and an arbitrary plurality number of subdivisions are flexibly allocated to respective user terminals. As such, in LTE, a high-speed wireless access environment is provided by effectively using limited frequency bands.
Further, in the link adaptation technique of LTE, a data modulation method can be flexibly altered according to a distance from eNodeB (an LTE wireless base station) to a user terminal, electric power, and the like. For example, in the link adaptation technique, the modulation method can be flexibly altered, ranging from QPSK (Quadrature Phase-Shift Keying) that is less susceptible to noise and interference to 64QAM (Quadrature Amplitude Modulation) that can transmit a lot of data by a single symbol. Thus, the link adaptation technique of LTE attempts to balance the performance and quality of communications by alteration of the modulation method.
In other words, according to the allocation of resource blocks and the link adaptation technique in a high-speed mobile communication environment, a wireless channel where frequency bands and radio field intensity are limited can be effectively used so as to provide a high-speed wireless access environment.
However, since the above-described respective techniques have technical contents of dynamically altering network resources that can be used by respective user terminals, there is inconvenience of highly frequently varying physical bands that have rarely varied in conventional techniques.
In TCP (Transmission Control Protocol) that has long been widely used in both wired or wireless data communications, a technique relating to a congestion control is advanced so as to cater to recent communication environments where a lot of traffics coexist.
In connection with this, delay-based TCP, represented by TCP Vegas (NPL 1), FAST TCP (NPL 2), can suppress a data transmission rate before a packet loss occurs by detecting congestion by analyzing the state of increased delay. In this way, such delay-based TCP can stabilize throughput without corrupting the network.
As other relating techniques, for example, the following technical contents (PTL 1 or 2) are known.
PTL 1 discloses a technical content where a mean relative delay increasing rate and a packet loss rate are calculated based on pre-generated statistical information, whereby occurrence of congestion is detected by comparing the mean relative delay increasing rate and packet loss rate with preset thresholds, as well as, a data reception rate is controlled based on this detection result.
Further, PTL 2 discloses a streaming device that sets a threshold according to a data distribution condition based on history information of reciprocating delay time that is measured upon a bit rate rise trial in the past and controls a bit rate based on the threshold. That is, this streaming device employs a technique in which a bit rate is controlled by detecting an appropriate threshold range based on history information of whether data could have been distributed with the raised bit rate, as well as, adjusting the threshold in levels within the range.